Overvoltage Spark Gaps from CPI EDB are a family of rugged ceramic-metal hermetically sealed switches or voltages ranging from 500 volts to 100 kV. These switches have peak current capabilities of up to 50 kA. They are ideal for protecting equipment from damaging high voltage surges when they are used in “crowbar” applications. They are also suitable for capacitor switching applications. The OGP- series offer the broadest operating range, while the PGP and PB series offer fast switching for high dv/dt applications. The PB series is intended for direct mounting on printed circuit boards.
Table 1 shows ratings for CPI’ OGP ceramic-metal overvoltage spark gaps when they are used in crowbar service. Note that for each “family” type, a range is shown for Static Breakdown Voltage (SBV); for any given gap, there can be only a single value for SBV.
For rating purposes, crowbar service is defined as being single-shot or very low repetition rate operation such that gap heating is nil. For applications where the various discharge parameters simultaneously approach the values shown, gap life will be on the order of 1000-5000 operations. Longer life can be obtained when operating at reduced power levels; alternatively, operation at higher levels is possible, but life will be reduced.
For applications involving repetitive operation such that gap heating is significant, the ratings of Table 2 apply. For discharge conditions simultaneously approaching the maximums shown, gap life is typically one million to five million operations. Again, a trade off exists between discharge severity and service life.
Table 3 shows ratings for CPI’ PGP and PB Series pulse overvoltage spark gaps. These have been specifically designed to protect critical components against damage caused by fast high voltage transients. The dynamic breakdown voltage (the voltage at which the gap breaks down under transient conditions) is a function of the rate of rise of the applied voltage (dv/dt). In general, it will be higher for higher dv/dt. The breakdown time of these gaps is much faster than that of conventional overvoltage types, and their dynamic breakdown voltage is relatively close to their static breakdown voltage over a wide range of operating conditions.
PGP Series: In single-shot protection service, these gaps can divert a transient energy as high as 10 joules and conduct a total charge as high as 300 millicoulombs. Dynamic breakdown voltage is typically less than twice their static breakdown voltage for applied voltage transients as fast as 300 kilovolts per microsecond.
Peak currents up to 1500 amperes with current rise times on the order of 1-5 nanoseconds are possible. The small size of these devices makes them well suited for use on circuit boards and in other applications where space is restricted. For best results the gap should be tightly coupled across the component to be protected. On nanosecond time scales, the inductive drop across even a few inches of excess wiring can easily exceed the rated turn-on voltage of the gap.
Typical rating for inter-electrode capacitance is 3 pf, dynamic voltage drop is 50 volts, and open circuit resistance at 500 volts is 1000 megohms.
| Family Type (1) | Available Static Breakdown Voltage Range (kV) Min-Max (2) | Peak Current (kA) | Total Conducted Charge per Pulse (millicoulombs) |
|---|---|---|---|
|
OGP-57 |
1-9 |
5 |
200 |
|
OGP-62 |
1-9 |
5 |
200 |
|
OGP-64 |
1-9 |
5 |
200 |
|
OGP-44 |
9-25 (3) |
5 |
200 |
|
OGP-49 |
2-25 (3) |
7.5 |
400 |
|
OGP-75 |
10-30 |
20 |
500 |
|
OGP-35 |
8-42 (3) |
50 |
1000 |
|
OGP-83 |
8-42 (3) |
25 |
800 |
|
OGP-67, 73 |
30-65 (3) |
20 |
500 |
|
OGP-76 |
30-120 (3) |
50 |
1000 |
|
OGP-1501 |
30-120 (3) |
50 |
1000 |
| Family Type (1) | Available Static Breakdown Voltage Range (kV) Min-Max (2) | Conducted Charge per Pulse (millicoulombs) | Avg. Current lb (mA, DC) (6) | RMS (Current IP) (A, AC) (7) |
|---|---|---|---|---|
|
OGP-57 |
1-9 |
4 |
40 |
6 |
|
OGP-62 |
1-9 |
4 |
40 |
6 |
|
OGP-64 |
1-9 |
4 |
40 |
6 |
|
OGP-44 |
9-25 (3) |
4 |
40 |
6 |
|
OGP-49 |
2-25 (3) |
8 |
60 |
8 |
|
OGP-75 |
10-30 |
20 |
150 |
10 |
|
OGP-35 |
8-42 (3) |
20 |
200 |
15 |
|
OGP-83 |
8-42 (3) |
8 |
100 |
10 |
|
OGP-67, 73 |
30-65 (3) |
20 |
150 |
10 |
|
OGP-76 |
30-120 (3) |
20 |
200 |
15 |
|
OGP-1501 |
30-120 (3) |
20 |
200 |
15 |
Notes
1. The general family type is listed. Mechanical variations with differing connections are shown in the accompanying drawings. These are designated by the addition of another digit or a letter to the basic family number. For example, the OGP-44 family includes the 44G, 441, 442, 443, 444, 445, 446, 44L and 44R.
2. Each overvoltage gap is manufactured with a specific static (or DC) breakdown voltage (SBV). this voltage can be set anywhere within the available min-max range. The SBV is specified by the addition of a dash number to the mechanical type number, giving the SBV in kilovolts.
3. These units must be operated in a dielectric medium to prevent external corona or breakdown: OGP-76, above 50kV; OGP-1501, above 35kV; OGP-44, above 15kV; OGP-67 and OGP-73, above 40kV; OGP-49, above 15kV; OGP-83 and OGP-35, above 20kV. Some of the more important derating factors that determine the safe operating voltage in air are the cleanliness of the tube’s ceramic insulators, the rate of rise of anode voltage, the dwell time at the operating peak anode voltage, the pulse repetition rate, and ambient pressure, temperature, humidity and contaminant level.
4. The ratings shown apply for single-shot service. Under these maximum duty conditions, gap life is typically 1000-5000 operations.
5. For conditions approaching these maximum ratings, life is typically one million to five million operations. Longer life can be obtained when operating at reduced levels; alternatively, operation at higher levels is possible, but life will be reduced.
6. Ib is the average current through the gap. It is equal to the conducted charge per pulse x pulse repetition rate (prr).
7. Ip is the RMS current through the gap. For rectangular current pulses, Ip = √Ib x peak current.