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Tunnel diodes: Difference between revisions
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== Applications == | == Applications == | ||
Tunnel diodes were used where it was | Tunnel diodes were mostly used where it was desirable to have fast and clean switching between two states. | ||
desirable to have fast and clean switching between two states. | |||
They were used in | They were used in | ||
* trigger circuits as Schmitt triggers, | * trigger circuits as Schmitt triggers, | ||
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* pulse generators for converting a slow-rise signals to fast-rise pulses, | * pulse generators for converting a slow-rise signals to fast-rise pulses, | ||
* countdown/sync circuits | * countdown/sync circuits | ||
However, tunnel diodes can also be used as oscillators and as amplifiers. There are different types of tunnel diode optimized for switching, oscillator or amplifier use. | |||
== Issues of Drift and Failure == | == Issues of Drift and Failure == | ||
Tunnel diode characteristics (peak and valley voltages and currents) tend to drift. Usually this can be handled by adjusting the surrounding circuit. Sometimes tunnel diodes completely fail. Replacement usually involves scavenging a similar tunnel diode from some other device. There are some people in the Tek community who may have some tunnel diodes they can sell. Germanium tunnel diodes are extremely sensitive to overheat, especially at soldering work. Be aware and use low melting solder and appropriate tool to protect the body from overheating! | Tunnel diode characteristics (peak and valley voltages and currents) tend to drift. Usually this can be handled by adjusting the surrounding circuit. Sometimes tunnel diodes completely fail. Replacement usually involves scavenging a similar tunnel diode from some other device. There are some people in the Tek community who may have some tunnel diodes they can sell. Furthermore, [[Russian tunnel diodes]] are still available from military surplus with relative ease. | ||
Germanium tunnel diodes are extremely sensitive to overheat, especially at soldering work. Be aware and use low melting solder and appropriate tool to protect the body from overheating! | |||
== Relevant Distinguishing Parameters == | == Relevant Distinguishing Parameters == | ||
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== Emulation using Common Parts == | == Emulation using Common Parts == | ||
A common question is whether an electrical equivalent to a tunnel diode can be made out of modern, | A common question is whether an electrical equivalent to a tunnel diode can be made out of modern, available parts. It is not hard to emulate the I-V curve (e.g. using a [http://en.wikipedia.org/wiki/Lambda_diode Lambda diode] circuit) but there is no known circuit that can be made from available parts that has right I-V curve at the low voltage level and high switching speeds of the real diode. | ||
available parts. It is not hard to emulate the I-V curve | |||
== Testing a Tunnel Diode == | == Testing a Tunnel Diode == | ||
Before concluding that a tunnel diode is bad, it is important to be sure that it has been measured correctly. A high resistance reading on a DMM indicates that the diode is bad. A low resistance on a DMM and a low voltage on a diode tester are both normal when measuring a tunnel diode. A more thorough test of a tunnel diode is to drive it through a resistor with a ramp voltage source while observing the voltage across the tunnel diode. The resistor should be calculated so that the peak current just exceeds the peak current that the tunnel diode is rated for. Of course if a curve tracer is available, it is great for measuring | Before concluding that a tunnel diode is bad, it is important to be sure that it has been measured correctly. A high resistance reading on a DMM indicates that the diode is bad. A low resistance on a DMM and a low voltage on a diode tester are both normal when measuring a tunnel diode. A more thorough test of a tunnel diode is to drive it through a resistor with a ramp voltage source while observing the voltage across the tunnel diode. The resistor should be calculated so that the peak current just exceeds the peak current that the tunnel diode is rated for. Of course if a curve tracer is available, it is great for measuring | ||
the I-V curve of the diode. | the I-V curve of the diode (note that plotting the negative resistance area may prove difficult or impossible). | ||
[[File:IV_Ge_TD-10mA.jpg|thumb|Tektronix 571 curve tracer run of 10mA tunnel diode.]] | [[File:IV_Ge_TD-10mA.jpg|thumb|Tektronix 571 curve tracer run of 10mA tunnel diode.]] | ||
[[File:Ge_TD.jpg|thumb|10mA tunnel diode mounted in Tektronix 571 curve tracer fixture.]] | [[File:Ge_TD.jpg|thumb|10mA tunnel diode mounted in Tektronix 571 curve tracer fixture.]] | ||