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Tunnel diodes: Difference between revisions
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Tunnel diodes are used in various timing circuits in Tek gear made from the early 1960's until the 1980's. 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. | Tunnel diodes are used in various timing circuits in Tek gear made from the early 1960's until the 1980's. 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. | ||
Many different types of tunnel diodes were made. The primary parameter that describes one is the peak current, which is the current at the top of the hill in the I-V curve. The other two relevant electrical parameters are the capacitance of the diode and whether it is made of GaAs or Ge. In some circuits, | |||
another model of tunnel diode can be substituted with only minor modifications to the surrounding circuit. Stan Griffiths describes such a modification here: | |||
* http://www.reprise.com/host/tektronix/reference/tunnel_diode.asp | |||
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, but there is no known circuit that can be made from available parts that has right I-V curve and the high switching speed of the real 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 | ||