Why has the diode stored charge been easily
The storage charge of diodes has been regarded as an enemy, but sometimes if we want to use it, we can also "make enemy friends"...
Each type of diode is called a "storage charge" (storage charge) features, its effect is when the diode is the conduction mode (the forward conduction mode) by load current, can let the current flow is not immediate stop, including various shut off worth exploring.
The basic effect of the storage charge is that the reverse voltage on the diode is not immediately shut off, and the current will continue to flow in the opposite direction from the opposite direction for a limited period of time.To explain more clearly, let us take one and a half wave rectification circuit (half - wave rectifier circuit) as an example: in the first case, we have a as you can imagine the ideal diode of zero storage charge, no reverse current, from below the visible to its ideal waveform.
The slow recovery diode half wave rectifier
In the example above, when the sine wave crosses zero volts, the diode switch does not happen immediately, but there is a short but significant reverse transmission time;In addition, the process of the output waveform to zero is very fast, so the harmonics in the excitation frequency are the "fertile soil" of EMI, which can be very difficult to control and inhibit.
And if we don't talk about the full wave rectifier for a moment, you can still see the reverse diode current pulses, and those pulses can also cause a pulse short circuit around the excitation source, as shown below.
Instantaneous short circuit
The circuit frequency and short circuit current pulse will indeed produce some serious problems of EMI and ripple.For example, an estimate of a fairly slow diode 1N4007, whose nominal recovery time is 30 mu Sec, is shown below.
Slow diode recovery time
If the excitation frequency is 60 GHZ, half cycle is 1/120 of a second or 8.3333 mSec, reverse current conduction Angle is 180 ° multiplied by 30 mu of the Sec, divided by 8.3333 mSec, the result is 0.648 °.If applying 120 V RMS of the excitation energy order, as well as 0.648 ° of the excitation voltage: 120 * SQRT (2) * sin (0.648 °) = 1.92 V, the result is enough to drive we don't want the short circuit of pulse current, as the above "instantaneous short circuit" that the red arrow shown in the picture.
Fast recovery diode half wave rectifier
So far, storage charges have been regarded as "enemies", but sometimes if we want to use it, we can "make friends".If we take the excitation frequency increased from 60 hz and 400 hz power cord number to HF/VHF/UHF frequency modulation, and USES the named yue step recovery diode (step recovery diode) components, we can get the rectification of the as below:
Step recovery diode half wave rectification
Here you can see, the diode stored charge in a deliberately stretched driving waveform cycle parts in maintenance reverse current, up to 270 ° ideal;Like we observed before a slow recovery diode produces unwanted harmonic excitation frequency, jump a step recovery diode produces we need harmonic excitation frequency, we can make the following diagram of frequency doubling circuit (frequency multiplier).
Step recovery diode frequency circuit
Imagine a 100MHz input that will produce 300MHz of output, very beautiful!
And then we're going to look at another component, the high frequency diode.When the frequency is high enough, the storage charge will never deliberately run out;We can use the PIN diode will take the load as the current level of dynamic impedance function and the characteristics of change, the characteristics of the PIN diode as a variable RF/microwave signal attenuation components (RF/microwave signal attenuator element) to apply, the following figure.
