Bridge rectifier
A single-phase diode bridge provides full-wave rectification: both halves of an AC cycle can drive the load with the same polarity. The unfiltered output is pulsating DC, not a regulated flat voltage.
Two diodes conduct in series with the load during each half-cycle; the other pair conducts on the opposite half-cycle. With a sinusoidal single-phase input, the ripple repeats at twice the input frequency: 100 Hz for 50 Hz or 120 Hz for 60 Hz. A reservoir capacitor reduces ripple, but diode voltage drops, charging pulses and load current affect the output.
In plain terms
A traffic roundabout for current: no matter which direction the flow tries to enter, the diodes route it out the same exit, so the load only ever sees one polarity.
Why designers use it
- Rectifying a suitable single-phase AC source without a centre-tapped winding.
- Providing a polarity-insensitive DC input when the forward loss is acceptable.
Best for
- Single-phase rectification
- Polarity-insensitive inputs
Key specifications
- Reverse voltage: Check repetitive reverse-voltage capability and transients
- Current: Distinguish average, repetitive peak and non-repetitive surge conditions
- Forward loss: Use voltage-versus-current and temperature data
- Thermal design: Check mounting, heat removal and junction temperature
- Switching: Check suitability for the actual source frequency
When not to use it
- When two forward drops create too much voltage loss or heat for the design.
- When the selected diodes' reverse recovery or other switching characteristics do not suit the frequency.
- As a substitute for mains isolation, regulation or product-level electrical safety.
Common mistakes
- Assuming the total forward drop is always exactly 1.4 V.
- Confusing average rectified-current, repetitive-peak and non-repetitive surge ratings.
- Ignoring reservoir-capacitor charging pulses and startup inrush.
- Connecting the bridge by package appearance instead of its marked terminals and manufacturer drawing.
Where you will find it
- UCSB's low-current bridge demonstration shows the two conducting pairs and the effect of different smoothing capacitors. Its 1N914 signal diodes are suitable for that experiment, not a universal power-rectifier choice.
- An LT4320-based active bridge drives four external N-channel MOSFETs to reduce rectification loss. It is a controller-based alternative, not four lossless diodes hidden in one package.
A short history
Bridge rectification can be built from discrete diodes or an integrated bridge module. A later implementation approach uses controlled MOSFETs to reduce conduction loss: Analog Devices documents this with the LT4320 family. The controller, external switches and operating conditions must all be selected together.
Good to know
- Only two of a four-diode bridge's diodes conduct in each ideal half-cycle.
- Full-wave single-phase ripple repeats twice per input cycle.
- An ideal-diode controller still needs real switches with resistance and thermal limits.