Voltage Doubler Symbol
Definition: The Voltage Doubler symbol represents a switched-capacitor or diode-capacitor charge-pump circuit block with two input terminals (In+ and In-) and two output terminals (Out+ and Out-) that produces an output DC voltage approximately twice the peak amplitude of the input AC or pulsed waveform, defined as a power conversion function under ANSI Y32.2 / IEEE 315 conventions as a labelled functional block.
Also known as: voltage multiplier, charge pump doubler, Greinacher circuit, Villard cascade (first stage), Cockcroft-Walton first stage, capacitive voltage doubler.
What the Voltage Doubler symbol means
The Voltage Doubler symbol denotes a circuit block that uses two diodes and two capacitors (in the classic half-wave Greinacher or Villard configuration) to charge a capacitor to the peak AC voltage during one half-cycle, then add that stored voltage in series with the next half-cycle peak, effectively doubling the output voltage. The full-wave Delon doubler uses a bridge arrangement to charge two capacitors, each to the peak voltage, and combines them in series to deliver twice the peak as DC output.
In schematic diagrams, the Voltage Doubler symbol is typically drawn as a rectangular functional block labelled with the stage gain (x2 or 2x) or part type, with In+ and In- on the left and Out+ and Out- on the right. The block communicates to the reader that the downstream circuit receives a supply voltage approximately double the input peak, useful when a higher supply voltage is needed but a transformer or switching converter is not available. The symbol may also appear as the full diode-capacitor ladder schematic when component-level detail is needed.
How to identify the Voltage Doubler symbol
The Voltage Doubler symbol is drawn as a rectangular block with four labelled terminals: In+ and In- (AC or pulsed DC input) on the left, and Out+ and Out- (doubled DC output) on the right. The block is labelled 'x2', 'Voltage Doubler', or with the specific circuit type (e.g. Greinacher, Villard, Delon). When drawn at the component level rather than the block level, the symbol shows two diodes (pointing in the charging direction) and two capacitors in the Greinacher or bridge configuration, using standard IEC or ANSI diode and capacitor symbols.
Function in a circuit
In a circuit, the Voltage Doubler converts an AC or pulsed input voltage to a DC output voltage of approximately twice the input peak amplitude. In the half-wave Greinacher circuit: during the negative input half-cycle, diode D1 conducts and charges capacitor C1 to the peak input voltage; during the positive half-cycle, the input voltage and the voltage stored in C1 add in series across diode D2, charging capacitor C2 to twice the peak voltage, which appears at the output. Under load, the output voltage is lower than 2 x Vpeak due to diode forward voltage drops (approximately 0.6-0.7 V per diode for silicon) and capacitor ESR losses.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 does not define a dedicated composite symbol for a voltage doubler circuit block; the function is represented as a labelled rectangular block per IEC 60617-02. When drawn at the component level, the diodes and capacitors use IEC 60617-05 (diode triangle-bar symbol) and IEC 60617-04 (capacitor two-bar symbol). |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 similarly treats the voltage doubler as a labelled functional block when drawn at the system level. At the component level, it uses ANSI diode (triangle-bar) and capacitor (two-plate) symbols. No dedicated voltage-doubler composite glyph is standardised. |
| Key difference | No unique glyph difference exists between IEC and ANSI for the voltage doubler block symbol. At the component level, the IEC version uses rectangle capacitors and triangle diodes; the ANSI version uses two-plate capacitors and the same triangle diode. The circuit topology is identical. |
Terminals / pins
| Pin | Name |
|---|---|
| in_pos | In+ |
| in_neg | In- |
| out_pos | Out+ |
| out_neg | Out- |
Typical values
Output voltage (no load, ideal): 2 x Vpeak of input. Output voltage (with load): 2 x Vpeak - 2 x Vf (diode drops) - ESR losses. Typical input frequency: 50/60 Hz (mains) to several MHz (switch-mode charge pump). Output ripple: inversely proportional to capacitor value and load current. Capacitor values: 0.1 uF to 1000 uF depending on output current and ripple requirements.
Where the Voltage Doubler symbol is used
- Generating a higher-voltage supply from a lower-voltage source without a transformer, common in isolated power supply designs
- CRT and vacuum tube anode high-voltage supplies in legacy electronics using AC mains input
- Bias voltage generation for MOSFET gate drivers requiring a voltage above V_CC
- Negative voltage rail generation for op-amp dual-supply circuits using a single positive supply and a voltage inverter variant
- Low-power charge pump ICs (e.g. MAX660, ICL7660) generating regulated doubled or inverted supply rails from 5 V
- Capacitive touch sensor circuits requiring a high-voltage sensing field from a low-voltage microcontroller supply
- Scientific instruments (Geiger counters, photomultiplier tubes) requiring hundreds or thousands of volts from a low-voltage input using Cockcroft-Walton multiplier stages
Example
In a low-power op-amp circuit powered by a single 5 V supply, a voltage doubler symbol (represented as a MAX660 charge pump IC block) appears between the 5 V rail and a -5 V rail needed for the op-amp. The In+ pin connects to 5 V, In- to GND, Out+ to GND, and Out- to the -5 V net. Two external 10 uF capacitors (one flying capacitor, one output reservoir) are shown connected to the IC pins as specified in the datasheet, enabling the dual-supply op-amp to swing its output through 0 V.
Key facts
- A Voltage Doubler produces an output DC voltage approximately equal to twice the peak input voltage, using two diodes and two capacitors in a charge-pump (Greinacher, Villard, or Delon) configuration without a transformer.
- The output voltage is less than 2 x Vpeak in practice due to diode forward voltage drops (approximately 0.6-0.7 V per silicon diode) and capacitor ESR losses under load current.
- The Voltage Doubler symbol is a four-terminal functional block (In+, In-, Out+, Out-) in schematics; at the component level it is drawn using standard diode and capacitor symbols.
- Voltage doublers can be cascaded to form voltage multipliers (Cockcroft-Walton ladder), producing n x 2 x Vpeak at n stages, used in particle accelerators and high-voltage power supplies.
- IEC 60617 and ANSI Y32.2 / IEEE 315 do not define a dedicated composite glyph for the voltage doubler; the block symbol is used at system level and component symbols at circuit level.
- The output ripple voltage of a voltage doubler is approximately I_load/(f x C), where f is the input frequency and C is the output capacitor value; increasing C reduces ripple.
- Integrated charge pump ICs (e.g. MAX660, ICL7660, LTC1044) implement voltage doubling or voltage inversion on a single chip, appearing in schematics as a labelled IC block with oscillator frequency set by an external capacitor.
Frequently asked questions
What does the voltage doubler symbol look like in a circuit diagram?
The voltage doubler symbol is a rectangular block with four labelled terminals: In+ and In- on the input side (left), and Out+ and Out- on the output side (right). The block is labelled 'x2' or 'Voltage Doubler'. When drawn at the component level, the symbol expands to show two diodes and two capacitors in the Greinacher or Delon configuration.
What does the voltage doubler symbol mean in a schematic?
The voltage doubler symbol means a charge-pump circuit is present that converts an AC or pulsed input to a DC output at approximately twice the peak input amplitude. It signals to the reader that the output rail has a higher voltage than the input, generated without a transformer.
How does a voltage doubler work?
A half-wave voltage doubler (Greinacher circuit) uses diode D1 to charge capacitor C1 to the negative peak voltage during the negative input half-cycle. During the positive half-cycle, C1's stored voltage adds to the input voltage, forward-biasing diode D2 and charging output capacitor C2 to approximately 2 x Vpeak, which appears as the DC output.
What is the difference between a voltage doubler and a voltage regulator?
A voltage doubler is a passive (or lightly active) charge-pump circuit that multiplies input voltage; its output changes with input amplitude and load current, and it provides no regulation. A voltage regulator actively maintains a fixed output voltage regardless of input variation or load current, dissipating the excess as heat.
Can a voltage doubler be cascaded for higher voltages?
Yes. Multiple voltage doubler stages can be cascaded in a Cockcroft-Walton multiplier ladder, each stage adding approximately 2 x Vpeak to the output. A three-stage multiplier theoretically produces 6 x Vpeak. Regulation degrades with each added stage due to accumulated capacitor losses and diode drops.
What standard defines the voltage doubler schematic symbol?
No dedicated voltage doubler composite symbol is defined in IEC 60617 or ANSI Y32.2 / IEEE 315. At the system level it is drawn as a labelled block; at the component level it is drawn using IEC or ANSI standard diode and capacitor symbols in the appropriate charge-pump topology.
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